Topic: "floating" roof-top mast invisible to lightning?

[wx_junkie]

Hi folks... I hope this will find a good number of readers in this category.

I'm going to be mounting a wireless weather stations sensor suite on my roof using a metal antenna tripod with a 10-foot mast (also metal).  My question to the group is, because the sensors are wireless and I am not running cables down and inside the house, or otherwise grounding the mast, is the mast for all intents and purposes "invisible" to lighting, or will I now have a lighting rod on my roof?

Here is my psuedo-scientific reasoning.  When a thunderstorm passes overhead, the bottom of the cloud is positively charged.  This in turn pushes any positive charge on the ground away, leaving a net negative charge.  Once the differential builds up to a certain point, the discharge happens as lighting, and usually to a tall object, as it is the closest path to the "negative ground".  But with my roof-top mast that is isolated (unless my asphalt shingles conduct when they get wet...), the positive cloud-base cannot push the positive charge on my mast away to net a negative charge, because there is no path for it to do so.  So in essence, it remains neutral, and I am no more likely to get struck.

Does this theory hold water at all?

Thanks very much,

Ray

[ArmySlowRdr]

Sounds good but I'm not too scientifically inclined.

Hopefully others will weigh in as I am about to move my anny up to the roof perimeter also using one of Ambients mounting arms with extension.  The anny looks made of plastic. just the poles are metal--about 7 feet are so in length. Is also wirless.

[WeatherHost]

or otherwise grounding the mast, is the mast for all intents and purposes "invisible" to lighting, or will I now have a lighting rod on my roof?

I believe you'll want the metal mast grounded.

You might want to look at 1-1/2" Schedule 80 PVC pipe and see if it will be strong enough to stay upright in your winds.

[wx_junkie]

I believe you'll want the metal mast grounded.

Thanks, but... you make no mention of the background behind this.  I could be completely wrong with my analysis and reasoning, and if so, I'm hoping someone can rationalize why and how.  But as I stand now, I see a grounded metal mast to be worse than an ungrounded one.

Ray

[ocala]

I can't answer your question but pretty much everything outside is prone to being hit by lightning. I don't know why your mast would be any different. From cows, trees, and homes, to planes, trains, and automobiles.
I don't think anything is lightning proof.
As for a lightning rod I would stay away from that. That attracts lightning.
Hopefully someone can answer your question.

[wx_junkie]

I can't answer your question but pretty much everything outside is prone to being hit by lightning. I don't know why your mast would be any different. From cows, trees, and homes, to planes, trains, and automobiles.
I don't think anything is lightning proof.
As for a lightning rod I would stay away from that. That attracts lightning.
Hopefully someone can answer your question.

Yup... understand and respect that everything is prone to getting struck, and my house is no different than any on my street.  I guess I'm trying to rationalize is that by adding an ungrounded 10-foot pole on top of my roof, I'm not tipping the scales out of my favor, so to speak, and thus am not MORE likely to get struck than before the mast was mounted.

Ray

[ocala]

I can't answer your question but pretty much everything outside is prone to being hit by lightning. I don't know why your mast would be any different. From cows, trees, and homes, to planes, trains, and automobiles.
I don't think anything is lightning proof.
As for a lightning rod I would stay away from that. That attracts lightning.
Hopefully someone can answer your question.

Yup... understand and respect that everything is prone to getting struck, and my house is no different than any on my street.  I guess I'm trying to rationalize is that by adding an ungrounded 10-foot pole on top of my roof, I'm not tipping the scales out of my favor, so to speak, and thus am not MORE likely to get struck than before the mast was mounted.

Ray

I would ask you this. Would you stand on your roof during a thunderstorm holding that same pole?

[Dr Obbins]

http://science.howstuffworks.com/nature/natural-disasters/lightning7.htm

[C5250]

Does this theory hold water at all?

It's not a theory, it's an hypothesis. And no it doesn't hold water.

There is no such thing as "isolated" at the charge potential that causes lightning. Air is not normally considered to be conductive, yet the charge from lightning is conducted by it. Lightning strikes trees, utility poles and chimneys all the time and can do quite a bit of damage to those objects because they are non-conductive. Lightning tends to strike the tallest objects (but not always). By grounding such an object you provide a low resistance path to ground, that (hopefully) will dissipate the strike with little or no damage. A non-conductive object will have a high resistance to the strike which will cause heat buildup, which often leads to the object melting or exploding. In the case of an ungrounded conductive metal pole as you suggest, the melting or exploding is likely to happen to whatever material the strike passes though after the pole on it's search for a path to ground.

[Aardvark]

My only comment in this topic.  There have been so many threads about grounding, not grounding, types of poles, wires and so forth  to debate once again, that anyone can search one more this once again, and beat it into the earth.

Will you be invisible to lightining,  no more than if you shed your clothes and streak through the church during Sunday High Mass. 

Strikes are random,  the higher the elevation into the strike zone the chances increase.   You get a direct hit, it is going to zap everything. All grounding will do is help direct the charge, if in the event  the strike hits your mast high up enough, there is a random chance with not great odds, that it will travel down the mast , down the ground wire and generate enough EMF that everything electronic around your house will make nice paperweights, suitable for gifts at holidays.

Go forth and perspire, may the farce be with thee, be fruitful and multiply or divide , add and subtract are viable options.

However, if you really want the correct answer, contact the physics department at your closest state university.

Shalom,

[SlowModem]

There have been so many threads about grounding, not grounding, types of poles, wires and so forth  to debate once again, that anyone can search one more this once again, and beat it into the earth.

I was thinking the very same thing (well, I didn't think of the pun.  Well done!    )

I was thinking that grounding was the only subject more discussed than GW on this forum.  (well, maybe cheese)

[Dr Obbins]

My old house was hit by lightening once. The TV antenna on the roof that was not necessarily the tallest point around, but the tallest with in about 1,000 feet. There were utility poles with in 300 feet. I had the co-ax cable coming down from the antenna across the roof and down the side of the house. Just before it went into the house there was a connector with a ground location. I ran a small gauge wire from it to a copper rod driven into the ground. I was not planning on lightening protection, just better TV reception.

Anyway the lightening found it. It was either a small bolt or just one of the locations it hit. The electricity traveled down the co-ax wire and then into the ground. But on it's way by my nightstand, some energy jumped through the wall and left a small burn mark on the wall by the outlet. There was a phone/answering machine plugged in at the time that got fried. Some stray electric must have made it's way through the house phone lines because the computer's modem in the living room got fried. The TV got it also. My Mom's house is located 2 houses up the street and she lost a TV.

I can't answer if the house would have gotten hit or not if the antenna wasn't there providing a ground. I do know that the electric current used the wire to get to the ground.

[wx_junkie]

I would ask you this. Would you stand on your roof during a thunderstorm holding that same pole?

Ok.. let's break this down. 

I would not stand on my roof without the pole in hand during a thunderstorm.  As for WITH the pole?  No, I would not do that either, as science fiction has "taught" us from early that it's not a smart thing to do.   But scientifically, is there a difference between standing on my roof with our without a pole during a thunderstorm.  Both are obviously stupid ideas, but is one more likely to receive a strike.  That's what I'm getting at...

[wx_junkie]

http://science.howstuffworks.com/nature/natural-disasters/lightning7.htm

Dr Obbins, thanks for that link, but it unfortunately does nothing to prove or disprove my current line of thinking.

[wx_junkie]

C5250 and Aardvark:

Thanks for your "meatier than average" replies.   I appreciate the time you have taken to reply with your thoughts.

I guess I'm still not totally getting my question answered. 

I understand that lightning strikes are random, and can occur anywhere.  I'm aware of that.   I live in a residential part of town that is fairly high up, and we've had lots of lighting strikes near by.  Last year, a house 2 doors down was struck and caught fire.  2 years before that, the light standard on the corner was hit, shattering the glass, and it took out my TV in the process (Hydro, Cable, Telephone are all buried, so I think it induces a current somewhere on my coax which fried my TV).  So anytime a thunderstorm happens by, I get a little nervous, even though I am weather nut / storm chaser, or whatever you want to call it.

I guess what I am trying to deduce is, if I put a 10-foot pole on my roof, am I MORE likely to get struck.  The last thing I want to do is put a "come get me" pole on my house, but for the reasons I highlighted in my OP, I can't for the life of me explain why the risk would increase.  Can it get struck?  Sure... but if I could re-wind and play out both scenarios, would my roof have gotten struck anyway, without the pole?

Thanks again for your time.

Ray

[Dr Obbins]

The more I think about this...Hmmm...

Now in the article I linked to it states "Many people believe that lightning rods "attract" lightning. It is better stated to say that lightning rods provide a low-resistance path to ground that can be used to conduct the enormous electrical currents when lightning strikes occur. If lightning strikes, the system attempts to carry the harmful electrical current away from the structure and safely to ground."

" The lightning can strike and then "seek" a path of least resistance by jumping around to nearby objects that provide a better path to ground. If the strike occurs near the lightning-rod system, the system will have a very low-resistance path and can then receive a "jump," diverting the strike current to ground before it can do any more damage."

My house and my mother's house both had TV antennas that were grounded and both were hit. The house in between us did not have an antenna and it did not get hit. The tall trees across the street did not get hit. I don't know if the power lines behind the house got hit or not. Lightening takes the path of least resistance so it went to the antennas that were grounded. If the antennas were not there, lightening would have still hit somewhere though. So the antennas acted like a lightening rod. They did not attract the lightening strike to the area, but did control where it went to some extent.

Are there other tall structures around your house? As mentioned, can you use a plastic pipe? To address your reasoning "So in essence, it remains neutral, and I am no more likely to get struck." I would focus on the word "more" and think that your are probably not more likely. And it appears that a grounded wire will put a "come get me" to an extent.

But then again, what do I know?   It's your house. Can you sleep at night?

[smorris]

if I put a 10-foot pole on my roof, am I MORE likely to get struck.

No.

According to meteorological consultant specializing in lightning safety Ronald L Holle, you will not increase or decrease your chances by grounding your equipment. As Aardvark already correctly answered, all you will do is ensure that *if* you get hit, that the grounding will help direct the current to the ground.

Watch CoCoRaHS webinar #6 for his comments on the subject. http://www.cocorahs.org/Content.aspx?page=wxtalk

[Aardvark]

C5250 and Aardvark:

Thanks for your "meatier than average" replies.   I appreciate the time you have taken to reply with your thoughts.

I guess I'm still not totally getting my question answered. 

I guess what I am trying to deduce is, if I put a 10-foot pole on my roof, am I MORE likely to get struck.  The last thing I want to do is put a "come get me" pole on my house, but for the reasons I highlighted in my OP, I can't for the life of me explain why the risk would increase.  Can it get struck?  Sure... but if I could re-wind and play out both scenarios, would my roof have gotten struck anyway, without the pole?

Thanks again for your time.

Ray

   No, it won't seek you out any more than Presidential elect committee looking for donations.   Let me ask you this, Why do you want a 10 foot pole on your roof?   We have had one chap fall off his room and was lucky only to have fractured a lot of bones on the second bounce.   What I would do is  put  a tripod on the ground, anchor it as I did with my system. The pole is 23 feet from the ground to the top.  I have anchored it into the earth with six , 5 foot threaded galvanized steel rods with nuts  on the top to anchor to the holes in the foot flanges of the tripod.  it is guy wired as well.  I have my ISS on that and a wireless unit also.

So far I have been blessed in 12 years not to have been zapped, yet.    I  only went 23 feet because I wanted to go 40 feet but my wife objected strongly and it occurred to me that one day I might need to take the unit down for repairs and getting it back up would be tough.

There are pictures on my site.   We have folks who have used a telescoping flag pole mount with great success as well, mounted into the ground.  Ground has two wonderful features... it is grounded, away from the house.   
  One thing to remember, you will someday need to make sure that your mast is perpendicular, you have to consider winds hitting the mast and how it is fastened to your roof will tear the boards and it gets wet when the roof comes off. YOu have a greater chance of wind damage than lightning damage.  The other factor is you have to go up on the roof. As you age, going up there periodically for maintaining it gets tougher and tougher.   

Consider a ground anchor instead.      here is the url to my station and you can see it and all the goodies. 
http://www.weatheraardvark.com/station_setup.htm

[WeatherHost]

What I would do is  put  a tripod on the ground, anchor it as I did with my system. The pole is 23 feet from the ground to the top.  I have anchored it into the earth with six , 5 foot threaded galvanized steel rods with nuts  on the top to anchor to the holes in the foot flanges of the tripod.  it is guy wired as well.

I  only went 23 feet because I wanted to go 40 feet but my wife objected strongly and it occurred to me that one day I might need to take the unit down for repairs and getting it back up would be tough.

That's what I did.  Mine is closer to 50', anchored at the ground, grounded with #6 Copper and guyed.  I rigged up a winch and pulley system so I can raise and lower it at will.

[kray1000]

If you have doubts about mounting anything on your roof, don't do it if there are other options.  If for no other reason, it will prevent you and your insurance company from arguing about whether your damage should be covered in the event of a strike to your home.  Aardvark and WeatherHost already suggested this, but I was going to suggest mounting everything on the ground as well.  I used a telescoping mast at my previous residence and it worked OK.

Even if grounding a mast would increase the chances of a strike (I believe it would, just my opinion), you should be more concerned about what would happen in the event of a strike.

For wireless installs attached to a building or deck, rather than using grounded metal, I prefer using stained pressure-treated 2x2 wood.

If you do decide on a metal mast on your roof, do a good job of grounding (personally, I would hire a pro, partly because I have a fear of heights.)  A weak ground (again, in my opinion) is worse than none at all.  Given your location, it sounds like you could benefit from having lightning rods installed on your home.  Growing up, we lived on a ridge and I slept a lot better knowing we had lightning protection in place.

[SoMDWx]

If that is the case, then what he is saying is that there is no need for grounding straps, grounding equipment, lightining rods, etc.

Anything that is metal can induce charges that building up on the surfaces. By grounding, you cause that mast to "de-energize".

True, if lightning hits this, there is nil chances that your stuff will survive, but by grounding, you drain off the charges on the mast, thereby reducing your chances. All relative......

Jim

if I put a 10-foot pole on my roof, am I MORE likely to get struck.

No.

According to meteorological consultant specializing in lightning safety Ronald L Holle, you will not increase or decrease your chances by grounding your equipment. As Aardvark already correctly answered, all you will do is ensure that *if* you get hit, that the grounding will help direct the current to the ground.

Watch CoCoRaHS webinar #6 for his comments on the subject. http://www.cocorahs.org/Content.aspx?page=wxtalk

[Moose Whisperer]

I believe you'll want the metal mast grounded.

Thanks, but... you make no mention of the background behind this.  I could be completely wrong with my analysis and reasoning, and if so, I'm hoping someone can rationalize why and how.  But as I stand now, I see a grounded metal mast to be worse than an ungrounded one.

Ray

I've been watching this thread with interest for  a while now. I don't want to weigh in on the whole lightning issue, because I'm not qualified to offer an educated opinion about the subject. However, there's another angle that might be of interest to you. I'm getting ready to install an RM Young 5103 anemometer on my station, and they are very adamant about the whole grounding issue in the installation manual:

Grounding the Wind Monitor is vitally important. Without proper
grounding, static electrical charge can build up during certain
atmospheric conditions and discharge through the transducers.
This discharge can cause erroneous signals or transducer failure.
To direct the discharge away from the transducers, the mounting
post assembly is made with a special antistatic plastic. It is very
important that the mounting post be connected to a good earth
ground. There are two ways this may be accomplished. First,
the Wind Monitor may be mounted on a metal pipe which is
connected to earth ground. The mounting pipe should not be
painted where the Wind Monitor is mounted. Towers or masts
set in concrete should be connected to one or more grounding
rods. If it is difficult to ground the mounting post in this manner,
the following method should be used. Inside the junction box
the terminal labeled EARTH GND is internally connected to the
antistatic mounting post. This terminal should be connected to
an earth ground (Refer to wiring diagram).

I don't know if other manuafacturers are specific about this issue, but I would think the same principles would apply. I just seems to me that a good ground makes sense from many different angles.

[C5250]

I guess what I am trying to deduce is, if I put a 10-foot pole on my roof, am I MORE likely to get struck.

It's much more complicated than that, but the simple answer would be yes. If your mast is higher than surrounding objects, it is more likely to be struck. OTOH, proper grounding of such a pole can do much to limit possible damage. Induced currents, especially when there is inadequate grounding is common and can cause much unexpected damage.